EP3107677A1

EP3107677A1 - Method and device for gas-shielded metal-arc welding using a non-consumable wire electrode and a consumable electrode

Info

Publication number: EP3107677A1
Application number: EP15714409.8A
Authority: EP
Inventors: Konstantin Alexander Büscher; Ralph WIJNHOLDS
Original assignee: MHIW BV
Current assignee: MHIW BV
Priority date: 2014-02-21
Filing date: 2015-02-17
Publication date: 2016-12-28
Anticipated expiration: 2035-02-17
Also published as: EP3107677B8; ES2675874T3; DE102014002213A1; HUE038406T2; CA2940201A1; DK3107677T3; DE102014002213B4; EP3107677B1; US20150239058A1; WO2015124286A1

Abstract

The invention relates to a method for gas-shielded metal-arc welding, wherein an arc burns in a shielding-gas environment between at least one workpiece to be welded and a consumable wire electrode (1) during the welding in order to produce a weld along a welding path, which wire electrode is fed continuously to the at least one workpiece. At the location of the start of the weld to be produced, a non-consumable electrode (2) is moved toward the at least one workpiece prior to the ignition of the arc between the at least one workpiece and the wire electrode (1). An arc is ignited in a shielding-gas environment between the at least one workpiece and the non-consumable electrode (2), by means of which arc the at least one workpiece is locally pre-heated at the start of the weld to be produced. After the pre-heating process, the non-consumable electrode (2) is pulled away from the at least one workpiece, and, after said non-consumable electrode (2) has been pulled away, the arc is ignited between the at least one workpiece and the wire electrode (1). The invention further relates to a torch head for performing the method.

Description

METHOD AND APPARATUS FOR METAL SAFETY GAS WELDING USING A NON-FLAVORING WIRE CHAIN AND A PLASTERING ELECTRODE

The invention relates to a method for metal-arc welding, wherein during welding to produce a weld along a

Welding path between at least one workpiece to be welded and a, in particular continuous to the at least one workpiece supplied consumable wire electrode an arc in a protective gas layer burns. The invention also relates to a burner head for metal inert gas welding.

Metal shielding gas welding, also referred to as MSG welding for short, is known in the prior art and has the advantages that the melting metal during welding to the workpiece, in particular continuously

supplied wire electrode as well as the refractory metal is protected by at least one workpiece to be welded during the welding process by a protective gas from the oxidizing ambient atmosphere.

It is also known that inert gas such as argon or helium can be used as a protective gas, wherein the welding process is then referred to as MIG welding or even that as protective gas an active or reactive inert gas, such as carbon dioxide or a Mixture of carbon dioxide and argon is used, which is then referred to as MAG welding. The selection of the respective inert gas is carried out essentially as a function of the material to be welded at least one workpiece.

Usually, burner units which have a wire feed for the wire electrode to be melted are used in these welding methods

1

CONFIRMATION COPY In this case, the wire electrode to be melted is passed through a current contact nozzle to direct the welding currents through the wire electrode. The Stromkontaktdüse in turn is arranged in a protective gas nozzle, which is usually formed sleeve-shaped, which is selected by this protective gas nozzle

Shielding gas is guided past the current contact nozzle and the wire electrode to the welding point, so that the local environment of the generated arc during

Welding is in a protective gas layer.

Metal shielding gas welding of this known type can be carried out both with manual guidance of a burner unit and also with automated guidance of a burner unit, wherein a weld seam following the welding path is usually produced by the movement of the burner unit along a welding path.

In the prior art, it is known that in metal inert gas welding in particular the beginning of the weld, which is also the time of the beginning of

Welding process corresponds, often has an insufficient penetration and therefore represents an insufficient connection between the at least one workpiece to be welded and the supplied from the wire electrode metal material or under two to be joined together

Workpieces.

In order to reduce this problem, it is especially when a burner unit is guided on a self-contained welding path, as is the case for example in butt welding of pipe ends, tried by a

Overlap between weld beginning and weld end the problem

to reduce lack of penetration at the beginning of the weld. Investigations of the beginning of the weld, for example by cutting and grinding samples, have shown, however, that even such overlapping welding does not completely solve the problem of lack of penetration in a MSG, in particular MAG welding. In the prior art, it has also become known to reflow a weld, which was produced by a MSG welding process, ie under inert gas or also active gas, without a welding filler

to add, namely for example by the fact that the weld seam with an ignited arc, which burns between the at least one workpiece to be welded and a non-consumable electrode, to run over.

Such a welding process, that with non-consumable electrode

is carried out, for example, the so-called TIG welding method in which a tungsten electrode is guided in a protective gas layer of inert gas after ignition of the arc on the previously produced in the MSG process weld. This is intended to bring about a remelting of the previously produced MSG, in particular MAG weld seam and thereby improve the penetration and equalize the weld. However, such methods prove to be complicated and costly due to the dual use of different welding processes.

From the document EP 1 583 359 a burner head for metal inert gas welding is also known, which comprises a first burner unit for

Feeding a consumable wire electrode and a second burner unit comprising a non-consumable stationary electrode, both

Burner units are mechanically connected to each other, the electrodes are arranged in a common, can be acted upon with protective gas protective gas nozzle and intersect the longitudinal extension directions of the electrodes, in particular cut at an acute angle.

According to this document, such a combined burner head is used to make a weld while performing MSG and TIG welding operations, this document describing that TIG welding processes lead the MSG process, that is, during the entire welding process for manufacturing a weld first the at least one workpiece by the between the at least one workpiece and the non-consumable electrode burning arc is melted and then fed in the subsequent MSG welding process material from a consumable wire electrode of the weld. Such a method using this known combined burner head is costly and technically complex, since both burner units of the combined burner head are continuously in operation during the implementation of a weld along a welding path and in this case the two simultaneously existing arcs can influence each other, so here special Measures of a technical nature for mutual shielding of the arcs must be made.

The object of the invention is a metal shielding gas welding process of the aforementioned generic type and also a burner head with

Burner units for both the supply of a consumable wire electrode and to hold a non-consumable electrode to improve insofar as the problem of lack of penetration at the beginning of a produced in the MSG process, in particular MAG process weld is overcome.

In a further development of the known method for metal-inert gas welding, this is inventively achieved in that at the location of the beginning of the weld to be produced temporally before the ignition of the arc between the at least one workpiece and the consumable wire electrode first in a preceding step, a non-consumable electrode to which at least one workpiece is moved, after which an arc is ignited between the at least one workpiece and the unmelting electrode moved thereon in a protective gas, in particular inert protective gas, with which the at least one workpiece is locally at the location of the weld to be produced

is preheated, wherein after the preheating the non-consumable electrode is pulled away from the at least one workpiece and is ignited after pulling away the arc between the at least one workpiece and the consumable wire electrode. The essential core idea of this method according to the invention is based on firstly local preheating of the at least one local welding of the at least one at the location of the beginning of a weld seam to be produced overall along a weld path, in particular also a closed weld path

Workpiece time to produce before the ignition of the arc between the at least one workpiece and the consumable wire electrode, so that then the subsequent use metal inert gas welding process in an already preheated area of the at least one workpiece, in particular of two joining together zenden workpieces.

In this case, a combined superimposition of two different welding methods, in particular no temporally superimposed existence of two, preferably at no time takes place in comparison to the above-described prior art

Arcs, as in the art of MSG and TIG welding processes, but at any time, only one of these is done

Welding method wherein the upstream welding with a non-consumable electrode under a protective gas atmosphere locally on the

Weld beginning remains limited.

For carrying out this method, the invention further provides a

Insert burner head, in which at the same time a first burner unit for supplying a consumable wire electrode and a second burner unit is provided with a non-consumable electrode, wherein the constructive development according to the invention provides that the burner unit not

melting electrode comprises a drive with which the non-consumable, in particular rod or needle-shaped electrode is displaceable in its longitudinal direction.

So here is not only the possibility to operate the two burner units with the different electrode units in time succession, but also continues to non-consumable electrode for performing a time subsequent MSG welding process along the weld to be created from the local area of influence of the arc between the melting wire electrode and the weld completely to remove, as with the

Device according to the invention, the non-consumable electrode advanced by means of the drive both in the direction of the workpiece and from

Workpiece can be withdrawn into the burner unit, in particular so that it is arranged completely outside the sphere of influence of the subsequently resulting arc of the other burner unit.

Preferably, it is provided here in a development that does not

Abschmelzende electrode, such as a tungsten electrode with preferably sharpened lower end, with said drive between two stop positions back and forth is movable, for which corresponding stops can be provided in the burner unit between which the non-melting

Electrode is movable.

In this case, it can provide in particular the invention that in one of the stop positions, namely the lower stop position, in which an arc is ignited at the non-consumable electrode, at the intersection of the

Longitudinal directions of both electrodes, so both the consumable wire electrode and the non-consumable electrode is located. This ensures that the non-consumable electrode is set at the beginning of the weld exactly to the local position of the at least one workpiece to be welded, at which time then the metal-shielding gas welding process using the abschmelzenden wire electrode begins.

Ignition of the arc at the non-consumable electrode can by high voltage pulses at an existing distance between the

Electrode tip and the at least one workpiece or by contacting the at least one workpiece and subsequent retraction of the electrode. The retraction can be done here by moving the entire Burner head or just move the electrode, for example, with the said drive.

After preheating, the non-consumable electrode is then withdrawn from the workpiece by means of the designated drive before starting the arc at the abschmelzenden wire electrode, in particular where already by retraction extinguishing the arc can be effected, or even with simultaneous or previous shutdown the power supply. Thus, the arc ignites at the melting point

Wire electrode always after the arc has not extinguished

melting electrode.

The burner head according to the invention may further provide that the burner unit of the non-melting electrode in the common

Shielding gas arranged closable, in particular with a

pivotable flap closable mouth opening, through which the tip of the non-consumable electrode is passed during movement between the stop positions.

Thus, for example, the invention may provide that upon movement into the lower position required for welding, the non-consumable electrode passes through the mouth opening, thereby displacing the pivotable flap from its closed position to an open position. Becomes

however, the non-consumable electrode withdrawn by the drive, it may provide the invention, for example by a spring load of

Flap that automatically closes the orifice again as soon as the tip with the non-melting electrode, the orifice in

Retreat direction has passed.

Thus, it can be ensured that an automatic closing of the mouth opening in the retracted position of the non-melting

Electrode is given and thus this electrode completely outside the Influence of the arc in the implementation of MSG welding is, therefore, for example, can not be contaminated by spattering welding beads.

The here named drive for moving the non-consumable electrode can basically be formed in any possible manner, for example by electric motor, hydraulically or pneumatically, whereby pneumatically not necessarily the use of compressed air, but generally of compressed gas, in particular using at least one In the welding processes used inert gas can be understood. Such a drive is preferably designed in each case as a linear drive, which causes a displacement in the linear direction along the extension direction of the non-consumable electrode.

A particularly preferred embodiment of the invention

Burner head may provide that the drive is designed as a cylinder-piston unit, which is operated in a further preferred embodiment with a gaseous fluid, such as with an inert protective gas, in particular such inert inert gas as argon or helium, which also for the implementation of the local preheating at the beginning of the weld or in addition to carry out the further welding can be used with abschmelzender wire electrode.

When using such a cylinder-piston unit, it can provide the invention that the non-consumable electrode in a displaceable

Plunger element of this cylinder-piston unit is arranged, for example, coaxially in this. Here can be a pinching in particular form and / or

non-positive attachment between the electrode and piston element may be provided.

Thus, by pressurizing the piston member by the gaseous fluid, such as an inert gas, movement of the piston member and thus movement of the non-consumable electrode may be generated. In this case, it can provide in principle the invention that the piston element of this cylinder-piston unit, for example, to two together

opposing piston surfaces in each case with pressurized, gaseous fluid can be acted reversibly, so that the direction of movement of the piston element depending on which results, which of each other

current piston surfaces is acted upon by pressure. Advancement or retraction of the non-consumable electrode can then be accomplished by merely switching the pressurization.

An alternative embodiment can also provide here that the piston element can be switched only on a piston surface with pressurized fluid

can be acted upon, for which this piston surface is located in a pressurizable piston chamber of the cylinder, and is displaced against a restoring spring force in this pressurization. If then the pressurization is switched off and the piston chamber, for example by valve actuation

depressurized, for example, to the outside environment, so the piston member and thus the non-consumable electrode by the spring force, which can be exerted by a compression spring, for example, is reset and this

in particular causes a movement of the non-consumable electrode away from the workpiece into the burner unit.

In the aforementioned embodiments, it can be particularly preferably provided that said cylinder-piston unit for driving the piston element off or switchable with an inert gas source, such as an argon or helium gas source is connected, with which at the same time the common inert gas supplied with inert gas or at least be supplied.

This ensures that the entire burner head system is always under inert gas influence even in the case of any structurally provided or possibly even in case of failure leaks and thus no oxidizing damage of the non-consumable electrode can occur. Particular preference is thereby achieved that by the same pressure gas source and the protective gas purging with inert gas for preheating the weld beginning according to the inventive method before the beginning of the MSG welding.

A further development of the method according to the invention can provide that, before the arc is ignited between the at least one workpiece and the non-consumable electrode, the wire electrode is withdrawn from the workpiece and then, after this retraction, the advance is not

melting electrode from the burner unit in the direction of the at least one workpiece takes place, the arc for local preheating at the beginning of the welding path temporarily, for example, ignited for less than 10 seconds and after extinction of this arc and in particular only after a

Retracting the non-consumable electrode again the consumable wire electrode is brought to the at least one workpiece.

Here it can be provided that when retiring the melting

Wire electrode this retraction takes place into the interior of the Stromkontaktdüse whereby it can be caused that the lower wire end of the

melting wire electrode while performing the preheating with the non-consumable electrode outside of its arc and associated influences.

A further development according to the invention can provide here that after the local preheating at the beginning of the welding path with a burner head, preferably provided in the burner unit of the consumable wire electrode

Measuring device is a determination of the wire tip position, in order to obtain from this information how far the consumable wire electrode for the start of MSG welding has to be advanced.

Even without such a measuring device can according to the invention a targeted

Advance take place, which, for example, in the feed rate is reduced to the normal feed rate during the MIG welding in dependence of the measured current, which rises sharply with the ignition of the arc.

The inventive method may further provide in a preferred embodiment that the ignition of the arc between the at least one workpiece and the consumable wire electrode takes place in a time interval in which a preheated area of the at least one workpiece at the beginning of the welding seam after the removal of the non-consumable electrode is present.

Here it can be provided, this time interval between extinction of the

Arc on the non-consumable electrode and the ignition of the

Arc at the melting wire electrode in the range of 1/100 to 200/100 seconds to choose. The time interval can be selected in a preferred embodiment so that the local temperature of the workpiece at the beginning of the seam does not fall below 400 degrees Celsius.

According to the invention, it is thus preferable to further ensure that with the drive described above a correspondingly rapid retraction of the non-consumable electrode from the welding position into the burner unit can take place, in particular so that the entire movement between the two stop positions, in particular during the retraction, takes a shorter time than the aforementioned maximum time interval between

Extinguishing and igniting the two aforementioned arcs at the two different electrodes.

It is thus ensured that a re-cold of the by not

produced melting electrode and the arc generated thereby

Workpiece preheating is avoided with certainty and thus the MSG welding process always starts when there is still a preheated area at the beginning of the seam to be produced. The invention preferably further provides that during the entire process step according to the invention, in which a local preheating is generated at the beginning of the weld by using an arc at the non-consumable electrode, the burner head according to the invention is in one

Resting position is located relative to the at least one workpiece, so therefore a driving movement of the melting wire electrode feeding

Burner unit or using the burner head according to the invention a driving movement of this entire burner head only after the extinction of the arc between the non-consumable electrode and the at least one workpiece and after starting the arc between the consumable wire electrode and the at least one workpiece begins. In particular, it may be provided here to provide a dwell time before the start of the travel movement, in which the weld beginning is welded by supplying the consumable wire electrode.

The inventive method can basically with any type of

Welding paths are used, wherein a preferred embodiment can provide the inventive method, in particular using the

burner head according to the invention to use in self-contained welding paths, since this can be done not only by improving the Einbrandes at the beginning of the weld seam rationalization of the weld and qualitative optimization, but also an overlapping welding between the weld end and weld beginning can be omitted when using the method according to the invention.

The welding method according to the invention, in particular using the burner head according to the invention can thus be used, for example, preferably for butt welding pipe ends both inside and outside, wherein it can be provided on the inside with the

according to the invention, to draw a weld and to provide on the outside a plurality of superimposed welds, wherein at least one, In particular, the lowest, but preferably all weld seams can be performed by the method according to the invention.

Particularly in the case of butt welding along a pipe circumference, both on the inside and on the outside, it may be provided to provide the respective pipe ends on the inside and outside with chamfers before abutting one another, wherein the inner chamfer may be smaller than the outer chamfer, so that one annular contact zone of the abutting pipe stumps or end faces is displaced radially inwardly over the middle of the pipe wall thickness. Thus, the smaller inner bevel of the abutting pipe ends forming the post-contact a V-groove, which can be closed with a single weld seam, wherein the forming, deeper, outer V-groove with a plurality, in particular at least two Schweißnahtlagen is closed.

By a preferred development of the burner head, according to which it comprises a first gas connection, in particular for supplying an inert gas, and a second gas connection, in particular for supplying an active gas, as well as a controllable valve device, by means of the alternatively the first or the second gas connection the protective gas nozzle is connectable, it may be preferably provided in the inventive process performed that during the arc between the non-consumable electrode and the at least one workpiece, a rinsing of the beginning of the weld through the protective gas with inert inert gas, such as argon or helium, takes place and rinse with active during the period of the arc between the consumable wire electrode and the at least one workpiece

Inert gas, in particular carbon dioxide or a mixture of carbon dioxide and argon, in particular wherein the gas supply is switched into the common shield after the extinction of the arc between the non-consumable electrode and the at least one workpiece from inert to active inert gas. Thus, welding along the welding path can be carried out as an MAG welding process, although the local preheating at the beginning of the weld was handled under inert gas influence, for example as a TIG welding process.

An inventive burner head, which can be used to carry out the method according to the invention, but not in its application

is limited solely to the implementation of this method will be explained in more detail with reference to the further described below Figure 1.

This figure 1 shows a burner head 6 of the type according to the invention, which here with respect to the illustration on the left side a burner unit 3, which is provided for performing a MSG welding process. Accordingly, the lower end of this burner unit 3 has a current contact nozzle 3a, through the bore of which a melting wire electrode 1 can be passed to form a current contact with this nozzle 3a.

At an angle α to the guide direction of the wire electrode 1 is a

Burner unit 7 is arranged, which has a non-consumable electrode, for example a tungsten electrode 2. This rod-shaped electrode 2 is displaceable by means of a drive 8 within the burner unit, in particular displaceable between two stop positions, which define the respective end positions of the displacement path. The displacement direction is here along the center line of the non-consumable electrode 2 and thus at the same aforementioned angle α to the guide direction of the wire electrode 1. This angle α is preferably an acute angle less than 45 °.

The inventive design of the burner head, it provides here that the tip 2a of the non-consumable electrode 2 in the lower stop position is preferably located exactly at the intersection 4 of the two mentioned guide directions of wire electrode and non-consumable electrode. The embodiment shown here provides that the drive 8 is formed by a cylinder-piston unit operated with compressed gas, in particular inert compressed gas, in which a piston element 8a is displaceable within the cylinder 8c. The execution described here illustrates that by a

Pressurization by the gas, in particular the inert gas such as argon or helium, in the annular space 8, the piston surface 8b is subjected to force and against a restoring force by the force acting on an opposite piston surfaces spring 11 is displaceable in the direction of the workpiece.

If the pressurization of the annular space 8d is switched off, for example, by switching over a valve and relieving the annular space with respect to the

Environment, so the piston member 8a, which is not coaxial here

holding the melting electrode, moved to the retracted position.

Holding the non-consumable electrode 2 in the piston element 8a can take place here, for example, by means of a clamping sleeve.

The figure 1 illustrates further here that in the illustrated position, the lower tip of the non-consumable electrode 2 has passed through a mouth opening 10 of the burner unit 7 and in this case has displaced a flap 9 in an open position. Here it provides the invention that the flap 9 a

Has spring load biasing the flap in the closed position, at the same time the flap 9 rests here on the electrode 2. It is thus caused by retraction of the non-consumable electrode 2 by the

Mouth opening 10 back into the burner unit, the flap 9 automatically

is closed and thus the electrode tip 2a of the non-melting

Electrode 2 comes to rest beyond any influence by an arc or a welding process of the burner unit 3.

The invention may basically provide that the cylinder-piston unit for moving the piston element with any gaseous pressure fluid, in

alternative embodiment is also operable with liquid fluid. When operating with gaseous pressurized fluid is further preferably provided to use as the working fluid, the inert gas, which is also used for flushing the printhead through the common shielding gas 5 while performing the preheating before beginning a MSG welding process with the consumable wire. 1

Although not visualized, the invention may provide for the burner head to have gas feeds for both an inert gas such as argon or helium, as well as an active gas such as carbon dioxide or a mixture of carbon dioxide and argon, by means of a switching valve the interior the protective gas nozzle 5 can alternatively be acted upon by the gas from one of the two gas supply lines.

It is therefore possible to carry out the local preheating at the beginning of a weld using the non-consumable electrode under inert gas purging, then switching off the gas supply of the shield 5 of inert gas to an active gas, as after extinguishing the arc from this non-consumable electrode Carbon dioxide or a mixture of carbon dioxide and argon from the other gas supply takes place.

For example, the subsequent inert gas welding process can be carried out under active gas as the MAG welding process. While maintaining the protective gas purging with inert gas on the other hand, it may be provided that the

perform subsequent MSG welding procedures as MIG welding.

It can be seen that with a burner head according to FIG. 1, preferably both welding processes with one burner unit 3 and with the other burner unit 7 can be carried out, in particular for carrying out the method according to the invention, in which welding, in particular local preheating by means of the burner unit 7 takes place only at the beginning of a weld and temporally upstream of the MSG welding process.

Claims

claims

Anspruch [en] A metal arc welding method in which an arc is fired in a protective gas environment during welding to produce a weld along a welding path between at least one workpiece to be welded and a consumable wire electrode (1) supplied continuously to the at least one workpiece, characterized in that

a. at the location of the beginning of the weld to be produced, a non-consumable electrode (2) is moved toward the at least one workpiece in time before the arc is ignited between the at least one workpiece and the wire electrode (1),

b. between the at least one workpiece and not

abschmelzenden electrode (2) is ignited in a protective gas surrounding an arc with which the at least one workpiece is preheated locally at the beginning of the weld to be generated, c. after preheating the non-consumable electrode (2) is pulled away from the at least one workpiece and

d. after withdrawing the non-consumable electrode (2), the arc between the at least one workpiece and the

Wire electrode (1) is ignited.

2. The method according to claim 1, characterized in that a

Preheating according to at least one of the following steps takes place: a. The preheating takes place up to a temperature below the

Conversion temperature of the structure of the at least one workpiece b. The preheating takes place up to a temperature below the

Melting temperature of the at least one workpiece and above a temperature at which a conversion of the structure of the at least one workpiece takes place c. The preheating takes place beyond a temperature beyond which the at least one workpiece melts.

3. The method according to claim 2, characterized in that the ignition of the arc between the at least one workpiece and the

Wire electrode (1) according to one of the following alternatives: a. Within n / 100 seconds after the extinction of the arc at the non-consumable electrode with n <100, preferably n <10 b. At a time when the at least one workpiece has reached a temperature below the transformation temperature, c. At a time, to which still a melt of at least one

Workpiece is present at the beginning of the weld.

4. The method according to any one of the preceding claims, characterized in that a driving movement in the welding direction of a the melting

Wire electrode (1) supplying burner unit (3) only after extinction of the arc between the non-consumable electrode (2) and the at least one workpiece and after starting the arc between the consumable wire electrode (1) and the at least one workpiece begins.

5. The method according to any one of the preceding claims, characterized in that before the ignition of the arc between the at least one

Workpiece and the non-consumable electrode (2), the wire electrode (1) is withdrawn and brought back to the at least one workpiece after extinction of this arc.

6. The method according to any one of the preceding claims, characterized in that the abschmelzende wire electrode (1) and the non-consumable electrode (2) on at an angle (a), in particular a pointed Angle (α) cutting paths are guided, in particular where the intersection (4) of both guideways

a. within the material thickness of the at least one workpiece to be welded or

b. exactly in the surface plane or

c. above the surface plane of the at least one workpiece to be welded.

7. The method according to any one of the preceding claims, characterized in that the abschmelzende wire electrode (1) and the non-consumable electrode (2) are moved within a common inert gas purged with protective gas (5).

8. The method according to claim 7, characterized in that during the duration of the arc between the non-consumable electrode (2) and the at least one workpiece rinsing of the beginning of the weld through the protective gas nozzle (5) with inert protective gas, in particular argon or helium takes place and during the duration of the arc between the consumable wire electrode and the at least one workpiece, a purging with active inert gas, in particular carbon dioxide or a

Mixture of carbon dioxide and argon takes place, in particular the

Gas supply to the common shielding gas nozzle (5) is switched from inert to active shielding gas after the arc has extinguished between the non-consumable electrode (2) and the at least one workpiece.

9. burner head (6) for gas metal arc welding comprising a first

Burner unit (3) for supplying a consumable wire electrode (1) and a second burner unit (7) with a non-consumable electrode (2), wherein both burner units (3,7) are mechanically connected to each other, the electrodes (1, 2) in one common, with inert gas

acted upon protective gas nozzle (5) are arranged and the

Cut longitudinal directions of the electrodes (1, 2), in particular at an acute angle (a) cut, characterized in that the burner unit (7) of the non-consumable electrode has a drive (8) comprises, with which the non-consumable electrode (2) is displaceable in its longitudinal direction.

10. Burner head according to claim 9, characterized in that the non-consumable electrode (2), in particular a tungsten electrode (2) with the drive (8) between two stop positions is reciprocable, in particular wherein in one of the stop Positions the tip (2a) of the non-consumable electrode (2) at the intersection (4) of

Longitudinal directions of both electrodes (1,2) is arranged.

11. Burner head according to one of the preceding claims 9 or 10, characterized

characterized in that the burner unit (7) of the non-consumable electrode (2) has a closable opening (10) which can be closed in the common protective gas nozzle (5), in particular with a pivotable flap (9), through which the tip (2a) of the non-consumable electrode (2) is guided in a movement between the stop positions, in particular wherein in one of the stop positions, the mouth opening (10) by applying a force, the flap (9) is automatically closed.

12. Burner head according to one of the preceding claims 9 to 11, characterized

in that the drive (8) is designed as a. A operated with a particular gaseous fluid cylinder-piston unit and the non-consumable electrode (2), preferably coaxially, in a displaceable piston member (8a) is arranged or b. An electromagnetic lifting drive, especially where not

melting electrode in a magnetic or

arranged magnetizable element that in one

electromagnetic, in particular reversible field is movable.

13. Burner head according to claim 12, characterized in that the

Piston element (8a) a. can be acted upon by switchover to two opposing piston surfaces with fluid under pressure or b. on a piston surface (8b) counteracting a restoring spring force (11) is acted upon with fluid under pressure switchable.

14. Burner head according to claim 12 or 13, characterized in that the cylinder-piston unit (8) for driving the piston element (8a) off or reversibly connected to an inert gas source, with which simultaneously the common shielding gas nozzle (5) with inert gas supplied or at least supplied.

15. Burner head according to one of the preceding claims 9 to 14, characterized

characterized in that the burner unit (3) of the melting

Wire electrode (1) comprises a measuring device for determining the wire tip position, in particular after a retraction movement of the wire electrode (1).

16. Burner head according to one of the preceding claims 9 to 15, characterized

characterized in that it comprises a first gas connection, in particular for supplying an inert gas and a second gas connection,

comprises in particular for supplying an active gas, and a controllable valve device, by means of which alternatively the first or the second gas connection to the protective gas nozzle (5) can be connected.